Octopus DNA reveals Antarctic ice sheet collapse 'near'

Scientists studying how Antarctica's ice sheets retreated in the deep past have turned to an innovative approach: studying the genes of octopuses that live in its cold waters.

New analysis It was published Thursday in the journal Science He found that geographically isolated groups of eight-limbed marine creatures interbred freely about 125,000 years ago, suggesting an ice-free corridor during a period when global temperatures were similar to what they are today.

The results indicate Western Antarctic Ice Sheet The authors said the WAIS system is closer to collapse than previously thought, threatening long-term sea level rise of 3.3 to 5 meters if the world cannot keep human-caused temperature rise to 1.5 degrees Celsius, the goal of the Paris Agreement.

As an evolutionary biologist focusing on marine invertebrates, “I understand and then apply DNA and biology as an indicator of changes that have occurred in Antarctica in the past,” lead author Sally Lau of James Cook University in Australia told AFP.

The Turquet octopus was an ideal candidate for the WAIS study, she said, because the species is found across the continent and basic information about it has already been answered by science, such as its 12-year lifespan and the fact that it emerged around four years ago. A million years ago.

They are about half a foot (15 cm) long excluding the arms and weigh about 1.3 pounds (600 grams), and lay relatively few but large eggs on the bottom of the seafloor. This means that parents must make great efforts to ensure that their offspring emerge – a lifestyle that prevents them from traveling far.

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They are also limited by swirling ocean currents, or eddies, in some of their modern habitats.

By sequencing DNA across the genomes of 96 specimens that were generally collected inadvertently as bycatch and then left in museum storage over a 33-year period, Lau and his colleagues found evidence of trans-westerly Antarctic sea lanes that once connected the Weddell, Amundsen and Ross Rivers. . Seas.

The history of genetic mixing suggests that the WAIS collapsed at two separate points — first in the mid-Pliocene, 3 to 3.5 million years ago, which scientists were already confident of, and the last time in a period called the last ice age, a warm spell. From 129,000 to 116,000 years ago.

“This was the last time the planet was about 1.5 degrees warmer than pre-industrial levels,” Lau said. Human activity, especially the burning of fossil fuels, has so far raised global temperatures by 1.2°C compared to the late 18th century.

“The tipping point in the future collapse of WAIS is near.”

There were a few studies before the new scientific paper that also suggested the WAIS collapsed at some point in the past, but they were far from conclusive due to the relatively low resolution of genetic and geological data.

“This study provides experimental evidence suggesting that the WAIS collapsed when the global mean temperature was similar to the present temperature, suggesting that the tipping point for future WAIS collapse is near,” the authors wrote.

A sea level rise of 3.3 meters would radically change the map of the world as we know it, submerging low-lying coastal areas everywhere.

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In an accompanying commentary article, Andrea Dutton of the University of Wisconsin-Madison and Robert DeConto of the University of Massachusetts called the new research “groundbreaking,” adding that it raises interesting questions about whether ancient history will be repeated.

However, they point out that several key questions remain unanswered – such as whether past ice sheet collapse was caused by rising temperatures alone, or whether other variables such as changing ocean currents and complex interactions between ice and solid land also played a role. .

It is also not clear whether sea level rise will continue over thousands of years or occur in more rapid jumps.

But such doubts cannot be an excuse for inaction against it Climate change “This latest evidence of octopus DNA stacks another card in an already unstable house of cards,” they wrote.

Latest news about ice in Antarctica

The study comes about a month after scientists confirmed that The largest iceberg in the world It was “on the move” after being stuck at the bottom of the ocean for 37 years, Friday. Recent satellite images show the eponymous iceberg A23aIt is now moving across the northern tip of the Antarctic Peninsula and heading toward the Southern Ocean, according to the British Antarctic Survey.

Earlier this month, the survey was released Dramatic video They were captured by the ship's crew, including drone footage that showed a pod of killer whales swimming next to the massive iceberg.

The iceberg weighs in Nearly 1 trillion tonsThis is according to data from the European Space Agency (ESA).

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The iceberg, with an area of ​​about 4,000 square kilometers (or 1,500 square miles), broke off the coast of Antarctica in 1986, but then settled in the Weddell Sea, the BBC reported. mentioned.

Meanwhile, in October, scientists revealed their discovery of a vast, hidden landscape of hills and valleys carved by ancient rivers that have been drilled. “Frozen in time” Under the Antarctic ice for millions of years.

“It's an unexplored landscape that no one has noticed,” said Stuart Jamieson, a glaciologist at Durham University in the United Kingdom and lead author of the book. the studytold Agence France-Presse.

The land beneath the East Antarctic ice sheet is less known than the surface of Mars, Jamieson said.

The area, spanning 32,000 square kilometers (12,000 square miles), was home to trees, forests and perhaps animals.

The ice came next and froze just in time, Jamison said.

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